We have recently described the presence of some factors in the rat lung cytoplasm which modulates the basal adenylate cyclase activity in membranes (Nijjar, M.S. (1979) Biochem. Biophys. Acta 584, 43-50). The proposed studies will examine the distribution and development of the modulator in other tissue and relate the findings to some cellular process. The modulator of adenylate cyclase will be purified from the rat lung cytoplasm by conventional techniques and characterized in terms of its physical and chemical properties. Its role in the regulation of basal- and hormonally-stimulated adenylate cyclase will be elucidated. The nature of stimulus which causes its appearance at a particular stage of development and whether it was newly sythesized or converted from a pre-existing inactive form will be examined. The significance of this modulator in the synthesis and secretion of surfactant and in cellular proliferation and differentiation will be investigated.